2 Answers
2

"Diplasiology” means “doubling” words; the Neoplatonic commentator Hermeias understood the term literally, as in “Alas, alas”; modern scholars tend to think words compounded of two roots are referred to.

Sorry I cannot help with the Greek roots, aside from pointing out that your guess on di- looks right, but maybe that definition will help point you to the right stem, too.

This is to complement @JeffSahol's answer. Apparently plasi- is from πλάσις, a molding or formation, which is from πλάσσω, "I mold" or "I form"; this is also the root of plastic and plasma; see the Free Dictionary on -plasia, a suffix used in medical terms such as dysplasia.